1. Field of the Invention
The invention relates to a process for the automatic adjustment of layered substrates, and more particularly the adjustment of semiconductor wafers by use of adjustment marks with optical alignment techniques.
2. Description of the Prior Art
It is known to produce structures in semiconductor surfaces by selective exposure and subsequent development of a photo resist layer arranged on the semiconductor surface. In a further process step, the zones of the surface layer to be structured and which are not covered with photo resist are etched away from the semiconductor surface. The photo resist layer is exposed at the zones either by means of contact printing or by means of projection printing. Contact printing is here defined as pressing a photo mask and the coated semiconductor wafer against one another. In projection printing, a 1:1 copy or a 1:10 reduction copy is produced by use of a high-resolution objective. Projection printing with 1:10 reduction possesses decided advantages, such as, for example, a high resolution of 500 lines/mm and a high adjustment accuracy of .+-. 0.2 .mu.m. Due to the lack of mechanical stress on mask and semiconductor wafer, it is possible to achieve defect free copies. A further advantage is the reduced testing expenses for mask control. Also the expansions or deflections of the semiconductor wafer have only a negligible influence on the alignment accuracy for consecutive structure planes. A disadvantage of this projection technique, however, is that the exposure of the entire semiconductor surface (e.g. 50 mm diameter) is very expensive since a plurality of adjusting and exposure steps are required.